Hematopoietic stem cells (HSC) have therapeutic potential as a result of their capacity to restore blood and immune cells in transplant recipients. Specifically, autologous or allogeneic transplantation of HSC can be used for the treatment of patients with inherited immunodeficient and autoimmune diseases and diverse hematopoietic disorders to reconstitute the hematopoietic cell lineages and immune system defense. Human bone marrow transplantation methods are currently used as therapies for leukemia, lymphoma, and other life-threatening diseases. For these procedures, a large number of stem cells must be isolated to ensure that there are enough HSC for engraftment. The number of HSC available for treatment is a clinical limitation. See U.S. Patent Publication No. 2010/0183564.
Prolonged pancytopenia is common following intensive chemotherapy regimens, myeloablative and reduced intensity regimens for hematopoietic cell transplantation (HCT), and exposure to acute ionizing radiation. Of particular concern is prolonged neutropenia, which results in a significant risk of infection despite improved antimicrobial therapy and increases morbidity and mortality. Thus, novel therapies that can abrogate prolonged pancytopenia/neutropenia following high dose chemotherapy and/or radiation, and potentially facilitate more rapid hematopoietic recovery, are needed.
2.1 Hematopoietic Stem Cells
The hematopoietic stem cell is pluripotent and ultimately gives rise to all types of terminally differentiated blood cells. The hematopoietic stem cell can self-renew, or it can differentiate into more committed progenitor cells, which progenitor cells are irreversibly determined to be ancestors of only a few types of blood cell. For instance, the hematopoietic stem cell can differentiate into (i) myeloid progenitor cells, which myeloid progenitor cells ultimately give rise to monocytes and macrophages, neutrophils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells, or (ii) lymphoid progenitor cells, which lymphoid progenitor cells ultimately give rise to T-cells, B-cells, and lymphocyte-like cells called natural killer cells (NK-cells). Once the stem cell differentiates into a myeloid progenitor cell, its progeny cannot give rise to cells of the lymphoid lineage, and, similarly, lymphoid progenitor cells cannot give rise to cells of the myeloid lineage. For a general discussion of hematopoiesis and hematopoietic stem cell differentiation, see Chapter 17, Differentiated Cells and the Maintenance of Tissues, Alberts et al., 1989, Molecular Biology of the Cell, 2nd Ed., Garland Publishing, New York, N.Y.; Chapter 2 of Regenerative Medicine, Department of Health and Human Services, August 2006, and Chapter 5 of Hematopoietic Stem Cells, 2009, Stem Cell Information, Department of Health and Human Services.
In vitro and in vivo assays have been developed to characterize hematopoietic stem cells, for example, the spleen colony forming (CFU-S) assay and reconstitution assays in immune-deficient mice. Further, presence or absence of cell surface protein markers defined by monoclonal antibody recognition have been used to recognize and isolate hematopoietic stem cells. Such markers include, but are not limited to, Lin, CD34, CD38, CD43, CD45RO, CD45RA, CD59, CD90, CD109, CD117, CD133, CD166, and HLA DR, and combinations thereof. See Chapter 2 of Regenerative Medicine, Department of Health and Human Services, August 2006, and the references cited therein.
2.2 Notch Pathway
Members of the Notch family encode large transmembrane proteins that play central roles in cell-cell interactions and cell-fate decisions during early development in a number of invertebrate systems (Simpson, 1995, Nature 375:736-7; Artavanis-Tsakonis et al., 1995, Science. 268:225-232; Simpson, 1998, Semin. Cell Dev. Biol. 9:581-2; Go et al., 1998, Development. 125:2031-2040; Artavanis-Tsakonas and Simpson, 1991, Trends Genet. 7:403-408). The Notch receptor is part of a highly conserved pathway that enables a variety of cell types to choose between alternative differentiation pathways based on those taken by immediately neighboring cells. This receptor appears to act through an undefined common step that controls the progression of uncommitted cells toward the differentiated state by inhibiting their competence to adopt one of two alternative fates, thereby allowing the cell either to delay differentiation, or in the presence of the appropriate developmental signal, to commit to differentiate along the non-inhibited pathway.
Genetic and molecular studies have led to the identification of a group of genes which define distinct elements of the Notch signaling pathway. While the identification of these various elements has come exclusively from Drosophila using genetic tools as the initial guide, subsequent analyses have lead to the identification of homologous proteins in vertebrate species including humans. The molecular relationships between the known Notch pathway elements as well as their subcellular localization are depicted in Artavanis-Tsakonas et al., 1995, Science 268:225-232; Artavanis-Tsakonas et al., 1999, Science 284:770-776; and in Kopan et al., 2009, Cell 137:216-233. Proteins of the Delta family and proteins of the Serrate (including Jagged, the mammalian homolog of Serrate) family are extracellular ligands of Notch. The portion of Delta and Serrate responsible for binding to Notch is called the DSL domain, which domain is located in the extracellular domain of the protein. Epidermal growth factor-like repeats (ELRs) 11 and 12 in the extracellular domain of Notch are responsible for binding to Delta, Serrate and Jagged. See Artavanis-Tsakonas et al., 1995, Science 268:225-232 and Kopan et al., 2009, Cell 137:216-233.
2.3 Notch Pathway in Hematopoiesis
Evidence of Notch-1 mRNA expression in human CD34+ precursors has led to speculation for a role for Notch signaling in hematopoiesis (Milner et al., 1994, Blood 3:2057-62). This is further supported by the demonstration that Notch-1 and -2 proteins are present in hematopoietic precursors, and, in higher amounts, in T cells, B cells, and monocytes, and by the demonstration of Jagged-1 protein in hematopoietic stroma (Ohishi et al., 2000, Blood 95:2847-2854; Varnum-Finney et al., 1998, Blood 91:4084-91; Li et al., 1998, Immunity 8:43-55).
The clearest evidence for a physiologic role of Notch signaling has come from studies of T cell development which showed that activated Notch-1 inhibited B cell maturation but permitted T cell maturation (Pui et al., 1999, Immunity 11:299-308). In contrast, inactivation of Notch-1 or inhibition of Notch-mediated signaling by knocking out HES-1 inhibited T cell development but permitted B cell maturation (Radtke et al., 1999, Immunity 10: 47-58; Tomita et al., 1999, Genes Dev. 13:1203-10). These opposing effects of Notch-1 on B and T cell development raise the possibility that Notch-1 regulates fate decisions by a common lymphoid progenitor cell.
Other studies in transgenic mice have shown that activated Notch-1 affects the proportion of cells assuming a CD4 vs. CD8 phenotype as well as an αβ vs. γδ cell-fate (Robey et al., 1996. Cell 87:483-92; Washburn et al 1997. Cell 88:833-43). Although this may reflect an effect on fate decisions by a common precursor, more recent studies have suggested that these effects may result from an anti-apoptotic effect of Notch-1 that enables the survival of differentiating T cells that would otherwise die (Deftos et al., 1998, Immunity 9:777-86; Jehn et al., 1999, J Immunol. 162:635-8).
Studies have also shown that the differentiation of isolated hematopoietic precursor cells can be inhibited by ligand-induced Notch signaling. Co-culture of murine marrow precursor cells (Lin− Sca-1+ c-kit+) with 3T3 cells expressing human Jagged-1 led to a 2 to 3 fold increase in the formation of primitive precursor cell populations (Varnum-Finney et al., 1998, Blood 91:4084-4991; Jones et al., 1998, Blood 92:1505-11). Incubation of sorted precursors with beads coated with the purified extracellular domain of human Jagged-1 also led to enhanced generation of precursor cells (Varnum-Finney et al., 1998, Blood 91:4084-91).
In a study of human CD34+ cells, expression of the intracellular domain of Notch-1 or exposure to cells that overexpressed Jagged-2 also led to enhanced generation of precursor cells and prolonged maintenance of CD34 expression (Carlesso et al., 1999, Blood 93:838-48). In another study, the effects of Jagged-1-expressing cells on CD34+ cells were influenced by the cytokines present in the cultures; in the absence of added growth factors, the interaction with cell-bound Jagged-1 led to maintenance of CD34+ cells in a non-proliferating, undifferentiated state, whereas the addition of c-kit ligand led to a 2-fold increase in erythroid colony-forming cells (Walker et al., 1999, Stem Cells 17:162-71).
2.4 Expansion and Engraftment of Hematopoietic Stem/Progenitor Cells
There is a need for successful expansion of human stem/progenitor cells (HSPC). This has particular immediate relevance for cord blood (CB) transplants where the stem cell dose in a single cord blood unit is often inadequate for a larger child or adult recipient and double cord blood transplantation (dCBT) is required. Despite dCBT for these individuals, engraftment is often delayed for more than 3 weeks leaving the recipient susceptible to infection resulting in increased morbidity and mortality (see Barker et al., 2005, Blood. 105 (3): 1343-1347). Thus successful ex vivo generation of both short- and long-term repopulating HSPC, including CB HSPC, has both biological relevance for better understanding HSPC self-renewal and clear clinical impact.
Past efforts have attempted to expand HSPC using soluble cytokine mediated methodologies; however, these attempts have demonstrated limited clinical efficacy (see Shpall et al., 2002, Biol Blood Marrow Transplant. 8(7): 368-376; de Lima et al., 2008, Blood. 112: Abstract 154; Jaroscak et al., 2003, Blood. 101(12): 5061-5067).
Varnum-Finney et al., 1993, Blood 101:1784-1789 demonstrated that activation of endogenous Notch receptors in mouse marrow precursor cells by an immobilized Notch ligand revealed profound effects on the growth and differentiation of the precursor cells, and that a multilog increase in the number of precursor cells with short-term lymphoid and myeloid repopulating ability was observed.
Delaney et al., 2005, Blood 106:2693-2699 and Ohishi et al., 2002, J. Clin. Invest. 110:1165-1174 demonstrated that incubation of human cord blood progenitors in the presence of an immobilized Notch ligand generated an approximate 100-fold increase in the number of CD34+ cells with enhanced repopulating ability as determined in an immunodeficient mouse model. See also U.S. Pat. No. 7,399,633 B2.
Delaney et al., 2010, Nature Med. 16(2): 232-236 demonstrated that a population of CD34+ cells obtained from a frozen cord blood sample, which population had been cultured in the presence of a Notch ligand (resulting in a greater than 100 fold increase in the number of CD34+ cells), repopulated immunodeficient mice with markedly enhanced kinetics and magnitude, and provided more rapid myeloid engraftment in humans in a clinical phase 1 myeloablative cord blood transplant trial.
Expansion techniques for cord blood stem cells have been described. See, e.g., U.S. Pat. No. 7,399,633 B2 to Bernstein et al., and Delaney et al., 2010, Nature Med. 16(2): 232-236. Delaney et al. reported rapid engraftment after infusion of previously cryopreserved cord blood stem cells which had been selected on the basis of HLA matching, and which had been expanded ex vivo.
International Patent Publication No. WO 2006/047569 A2 discloses methods for expanding myeloid progenitor cells that do not typically differentiate into cells of the lymphoid lineage, and which can be MHC-mismatched with respect to the recipient of the cells.
International Patent Publication No. WO 2007/095594 A2 discloses methods for facilitating engraftment of hematopoietic stem cells by administering myeloid progenitor cells in conjunction with the hematopoietic stem cell graft, for example, where the hematopoietic stem cell graft is suboptimal because it has more than one MHC mismatch with respect to the cells of the recipient patient.
U.S. Pat. No. 5,004,681 to Boyse et al. discloses the use of human cord blood stem cells for hematopoietic reconstitution.
U.S. Patent Publication No. 2010/0183564 to Boitano et al. discloses methods and compositions for expanding HSPC populations using an agent capable of down-regulating the activity and/or expression of aryl hydrocarbon receptor and/or a downstream effector of aryl hydrocarbon receptor pathway.
International Patent Publication No. WO 2011/127470 A1 discloses methods and compositions for providing hematopoietic function to a human patient, by selecting an expanded human umbilical cord blood stem/progenitor cell sample without taking into account the HLA-type of the expanded human cord blood stem cell/progenitor sample or the HLA-type of the patient, and administering the selected expanded human cord blood stem/progenitor cell sample to the patient; as well as methods for obtaining the expanded human cord blood stem cell/progenitor cell samples; and banks of frozen expanded human cord blood stem cell/progenitor cell samples, and methods for producing such banks.
International Patent Publication No. WO 2011/127472 A1 discloses methods and compositions for providing hematopoietic function to a human patient, by selecting a pool of expanded human umbilical cord blood stem/progenitor cell samples for administration to a patient, wherein the samples in the pool collectively do not mismatch the patient at more than 2 of the HLA antigens or alleles typed in the patient, and administering the selected pool of expanded human cord blood stem/progenitor cell samples to the patient; as well as methods for obtaining the pools of expanded human cord blood stem cell/progenitor cell samples; and banks of frozen pools of expanded human umbilical cord blood stem cell/progenitor cell samples, and methods for producing such banks.
2.5 Effects of Aryl Hydrocarbon Receptor Antagonist on Cell Expansion and Engraftment
Boitano et al. described enhanced ex vivo expansion of CD34+ cord blood HSPC with StemRegenin1 (SR1), an aryl hydrocarbon receptor (AhR) antagonist that acts at least in part by preventing cellular differentiation resulting in HSC expansion (see Boitano et al., 2010, Science 329(5997): 1345-1348). Specifically, Boitano et al. demonstrated that culturing HSPC with SR1 leads to a 50-fold increase in CD34+ cells and a 17-fold increase in the number of cells with the ability to repopulate immunodeficient mice. Boitano et al further demonstrated that these SR1-mediated effects are direct result of inhibition of AhR present on HSPC.
Citation or identification of any reference in Section 2 or any other section of this application shall not be construed as an admission that such reference is available as prior art to the present invention.